The present invention relates to an apparatus for monitoring the amount of radioactive rare gases such as .sup.3 H, .sup.14 C, and .sup.85 Kr in effluent gas discharged from nuclear facilitates.
Effluent of radioactive waste material from a nuclear power plant or other facilities which handle radioactive substances must be strictly monitored to protect our environment from radioactive pollution. Accordingly, techniques are demanded for measuring at very low levels the concentration of the radioactive substance contained in the material released from these facilities or in the surrounding environment. In particular, .sup.3 H, .sup.14 C, and .sup.85 Kr are nuclides which have long half-lives even at low concentration. Therefore, their concentration must be measured and monitored even at very low concentrations.
A conventional effluent gas monitoring apparatus has been proposed in which are serially arranged an oxidizing section, a water separating section, a carbon dioxide separating section, and, if necessary, a rare gas concentrating section. Part of the effluent gas from the nuclear facility is introduced to the oxidizing section where carbon monoxide, hydrogen, hydrogen carbide and so on contained in the gas are converted to water and carbon dioxide. The oxidized gas is introduced to the water separating section where the water in the gas is solidified or condensed by cooling for separation. The gas from which water has been removed is introduced to the carbon dioxide separating section and is passed through a carbon dioxide absorbing solution such as monoethanolamine or the like to separate the carbon dioxide in the gas by absorption. The separated water and carbon dioxide are recovered and are measured for their respective .sup.3 H and .sup.14 C contents by liquid scintillation counters. If necessary, the gas from which the water and carbon dioxide has been separated is introduced to the radioactive rare gas concentrating section to concentrate .sup.85 Kr or the like for measuring the concentration thereof.
However, since the water separating section, the carbon dioxide separating section, and the rare gas concentrating section are serially arranged with such a conventional apparatus, the flow rates and capacities of each section may not be determined independently of each other. For example, when the effluent gas is passed through the rare gas concentration section at a flow rate necessary for measuring .sup.85 Kr, this flow rate becomes higher than the optimum flow rate for the water separating section and for the carbon separating section. Thus, for obtaining better efficiency, the capacity or scale of the apparatus must be increased. Although the optimum flow rate at the water separating section changes according to the time of year and weather conditions, the flow rate at this section cannot be changed independently of the other sections with the serial arrangement. Furthermore, the amine-type absorbing solution such as monoethanolamine or phenylethylamine used for absorption of carbon dioxide becomes mixed with the exhaust gas from the carbon dioxide separating section and is then adsorbed or condensed within the next rare gas condensing section and might cause corrosion, particularly of rubber parts. Since these amine-type absorbing solutions are toxic, direct release into the air of the exhaust gas containing them poses an environmental pollution problem. As for the monoethanolamine, it is known to cause disorders in skin, mucous membranes and respiratory organs. LD.sub.50 for rats is reported to be 2,140 mg/kg in the case of oral administration and 981 mg/kg in interperitoneal administration.